Activation of rat masticatory muscle afferent fibres by acidic pH. (3rd April 2018)

• Record Type: Journal Article
• Authors: Gazerani, Parisa; Cairns, Brian Edwin
• Is Part Of: Somatosensory & motor research. Volume 35:Number 2(2018)
• Page Start: 86
• Page End: 94
• Publication Date: 2018-04-03
• Subjects: Acid sensing ion channel -- hypertonic saline -- immunohistochemistry -- masticatory muscle -- nociceptor; Skin -- Innervation -- Periodicals; Somesthesia -- Periodicals; Perceptual-motor processes -- Periodicals; 573.85
• DOI: 10.1080/08990220.2018.1473246
• Languages: English
• ISSNs: 0899-0220

Abstract

Abstract: Previous research findings have suggested an important role for acid sensing ion channels (ASICs) in muscle pain mechanisms. This study was conducted to determine if masticatory muscle afferent fibres express ASICs, if there are sex differences in this expression, and to compare the effects of low pH and hypertonic saline on afferent fibres that innervate the masticatory muscle in vivo . Immunohistochemistry methods were applied to examine the expression of ASICs in trigeminal ganglion neurons, while in vivo electrophysiology techniques were employed to examine changes in masticatory muscle afferent fibre excitability. Both ASIC1 and ASIC3 were expressed by predominantly larger masticatory muscle ganglion neurons, but the frequency of ASIC3 expression (56%) was significantly greater than ASIC1 (35%). No sex-related differences in expression were identified. Injection of pH 5.8, but not pH 6.8, phosphate buffered saline evoked afferent discharges that were significantly greater than those evoked by pH 7.4 buffer (control). Since ASIC3 channels are not activated until the pH is around 6, these results indicate that activation of both channels contributes to excitation of masticatory muscle afferent fibres. The results further show that many masticatory muscle afferent fibres, which respond to low pH, are low threshold mechanoreceptors. These findings may explain why injection of low pH solutions into the masticatory muscles of healthy humans is not associated with significant muscle pain.